Getting the "Tree View" Dialog Box

May I ask what do you call the "Dialog Box" that pops up if you click a button say, "Browse" which shows all the files in the file System and then you select a folder, click OK and all of its contents will be retrieved? Its like in WinAmp music player where you want to add file/folders then you click a button, a dialog box will appear, then you select a folder, click OK and then the contents of that folder will be retrieved.